There has been the need for high temperature ceramic materials in powdered form where the particle size of the powder is very small, e.g. submicron size. The ceramic powders in the submicron size, where the average particle size is less than 1 micron, are especially required for sintering operations where the powders are sintered into high temperature high strength ceramic articles. One such ceramic article that is often used for its strength is silicon carbide fibers. The strength, toughness and other properties of silicon carbide fibers are determined by their microstructure which is controlled by the manner in which they are made.
Silicon carbide fibers can be prepared by extrusion and spinning of plasticized mixtures of powder with subsequent sintering. If the silicon carbide powders used in the fiber making, contain particles substantially greater than 1 micrometer, the fibers when formed by spinning exhibit a rough surface. During deformation of the plasticized powder during shaping of the fiber, the particles are displaced and rotated causing the formation of pits and asperities in the surface. This surface roughness generated during the spinning operation is essentially preserved in sintering. There is little or no smoothing of the fiber surface by mass transport in the sintering operation. Consequently, the surface pits are sharp edged to their roots. This makes the surface pits on the fibers undesirable stress risers which may limit the tensile strength of the silicon carbide fiber.
There is a need to provide a silicon carbide fiber having a surface with reduced pits and asperities and improved strength. There is further a need to provide a silicon carbide fiber made from fine submicron size powder that provides a dense, small grain microstructure.